Advantages of using coverboards

Of the three insulations discussed in the presentation: expanded polystyrene, extruded polystyrene, and polyiso, the R-value of the polyiso is most affected by moisture intrusion. In addition, the polyiso will deform after prolonged exposure to moisture. For these reasons, it is recommended to install a fiberglass mat-faced or cementitious hard coverboard.

Using plywood on the roof-side of the parapet is a common installation when dimensional stability and fire ratings are not required. It is recommended to verify with the system manufacturer what substrates are approved with the specified system.

Yes, Factory Mutual (FM) requirements only apply to buildings they insure. However, their requirements have become industry design standards for all commercial roof assemblies, regardless if the roof is insured by FM.

Long-Term Thermal Resistance (LTTR) is related to R-value. LTTR represents a product’s average thermal resistance over a 15-year period while R-value is the value of thermal resistance for the product as a new product. For detailed information on this LTTR value, refer to THIS article on Polyisocyanurate Insulation Manufacturers Association’s (PIMA) website. The R-value of each DEXcell® Roof Board is published on each product submittal sheet.

The thickness of the coverboard is determined by the architect, roof consultant, and system manufacturer based on specific project requirements and roof systems. Some considerations for using a thicker board are; flute spanability, thermal protection, acoustics, severe hail areas, and when a vapor barrier is specified in the system.

Currently, there are several options available for multi-ply systems (mod-bit) including DEXcell FA Glass Mat roof boards for both adhered and mechanically attached systems. The redundancy of layers in a multi-ply system offers a greater opportunity to protect the membrane and the insulation below, especially in adhered systems. It is significant that DEXcell FA is also listed in mechanically attached systems because protecting the membrane over the fastener and plate is difficult. Single-ply systems are much more difficult to protect from hail damage. Options currently being tested and explored include OSB, plywood, mineral fiberboard, and glass mat roof boards.

No, there are no specific requirements to add more coverboard layers. However, if an increased acoustical value of the system is needed then adding mass helps to increase the STC/ OITC value. Refer to pages 20-21 of the DEXcell Roof Board Technical Guide for more information on STC/ OITC rated assemblies.

Yes, the system attachment method dictates the proper products for the assembly. The best product to use as a thermal barrier in a roof system is DEXcell Cement Board because it is unaffected by moisture. DEXcell Glass Mat and DEXcell FA Glass Mat are both available as Type X products in 5/8” thickness and can be used in fire-rated roof-ceiling assemblies.

DEXcell Glass Mat and DEXcell FA Glass Mat flute spans range between 2-5/8 to 8 inches and DEXcell Cement Board flute span is 12 inches.

In addition to weather-related events, coverboards protect an owner’s roof system investment. Coverboards reduce the impact of human foot traffic on insulation due to routine maintenance and equipment installations. System failures often occur where equipment has penetrated the roof membrane system. Utilization of a moisture-resistant, hard coverboard can help mitigate the negative effects of moisture intrusion into the roof assembly. Coverboards contribute to the longevity of the roof by protecting the roof membrane above it and everything in the system under it.

Fiberglass mat gypsum coverboards have a high compressive strength compared to most coverboard options. DEXcell Glass Mat and DEXcell FA Glass Mat coverboards have a compressive strength of 900 psi.

Each thickness of fiberglass mat coverboards have a different bending radius. Refer to the submittals for each product for guidance, DEXcell Glass Mat Roof Boards have a bending radius of four to six feet depending on the thickness. In addition, the DEXcell Cement Board has a published bending radius of five feet. These tight bending radii give the consultant and contractor design and installation options. Barrel roofs are a great opportunity for the use of fiberglass mat and cementitious roof boards.